Photochromism is a phenomenon which has drawn attention for the last several years, and refers to a reversible action in which a certain compound rapidly changes its color when irradiated with a light containing ultraviolet rays, such as sunlight or light from a mercury lamp and returns to its original color when the irradiation is stopped and the compound is placed in a dark place. Compounds having this property are called photochromic compounds. Photochromic compounds of various structures have been synthesized and proposed, but no particular common skeleton has been observed in the structures.
Understanding the above background, JP-A Sho 60-155179 discloses a photochromic compound represented by the following general formula: ##STR4## [wherein the group ##STR5## is an aromatic group, an unsaturated heterocyclic group, or a heterocyclic group in which a benzene ring is fused; and
R.sup.4 is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group or a heterocyclic group; PA1 Y is an oxygen atom or ##STR6## (wherein R is a hydrogen atom, an aryl group, an alkyl group or an aralkyl group)] and its use in a photoreactive lens. PA1 R.sup.1 is a monovalent hydrocarbon group or a monovalent heterocyclic group each of which may have a substituent(s); PA1 R.sup.2 is an electron-attracting group; PA1 R.sup.3 is an alkyl group, an aryl group, an amino group, an alkoxy group or an electron-attracting group; PA1 n is an integer of 0 to 4; and when n is an integer of 2 or more, a plurality of R.sup.3 s can be atoms or groups that are different from each other]. PA1 R.sup.9 is an alkylene group having 1 to 4 carbon atoms or a group represented by the following formula: ##STR28## (wherein R.sup.10 is an alkylene group having 1 to 4 carbon atoms, PA1 Hal is a halogen atom; PA1 l and p are each an integer of 0 to 10, and PA1 q indicates the number of the halogen atoms substituted and is an integer of 0 to 4), and PA1 m is an integer of 1 to 10], and monomers represented by the following general formula (V): ##STR29## (wherein R.sup.8 is a hydrogen atom or a methyl group, R.sup.11 is an ethylene group or propylene group, r is an integer of 0 to 10, s is 0 or 1, t is an integer of 0 to 2, and R.sup.12 is a hydrogen atom, a hydroxymethyl group or a lower alkyl group such as methyl group, ethyl group or the like). In the present invention, the term "(meth)acrylate" is a general term for methacrylate compound and acrylate compound. PA1 R.sup.19 and R.sup.20 may together form a ring; and PA1 R.sup.22 and R.sup.23 may together form a ring; PA1 R.sup.21, R.sup.22 and R.sup.23 may each have a substituent;
The following compound is disclosed in the Examples of this literature as a specific photochromic compound: ##STR7##
Also, JP-A Hei 2-28154 and U.S. Pat. No. 4,882,438 corresponding thereto disclose a fulgide or fulgimide compound represented by the following general formula: ##STR8## [wherein the group ##STR9## is a divalent aromatic hydrocarbon group or a divalent unsaturated heterocyclic group each of which may have a substituent (s); R.sup.5 is a monovalent hydrocarbon group or a monovalent heterocyclic group each of which may have a substituent(s); the group ##STR10## is a norbornylidene group or an adamantylidene group each of which may have a substituent(s); and Y' is an oxygen atom, ##STR11## The fulgide or fulgimide compound has an excellent photochromic property because it remains stably colorless under normal condition, quickly develops a color when irradiated with sunlight or ultraviolet rays, returns to a colorless state when the irradiation is stopped, and repeats the above color change with good durability. The following compound is disclosed in the Examples of this literature as a specific fulgide or fulgimide compound: ##STR12##